50 kW vs 100 kW vs 250 kW: choosing a commercial solar system size
In short
The size classes are separated by continuous and peak demand, not by building size. A 50 kW class system suits sites peaking around 40–60 kW; 100 kW suits peaks around 70–100 kW; 250 kW is a different design conversation entirely — usually PV with generator or grid support, where storage is sized per project. The converter rating disqualifies a size class faster than the roof does.
The short answer
Take your highest 15- or 30-minute average demand from the meter. Below about 60 kW peak, you are in the 50 kW class. Between roughly 70 and 100 kW, the 100 kW class — and this is where our documented 100 kW / 215 kWh reference configuration sits. Above that, you are comparing a multi-unit PV design, where the converter arrangement and storage strategy need engineering before any number is meaningful.
Configuration and comparison
| Dimension | 50 kW class | 100 kW class | 250 kW class |
|---|---|---|---|
| Peak demand it fits | Roughly 40–60 kW | Roughly 70–100 kW | Roughly 150–250 kW |
| Typical daytime consumption | 200–400 kWh/day | 400–800 kWh/day | 1,000–2,000+ kWh/day |
| Roof area for the PV | ~250–350 m² | ~500–700 m² | ~1,300–1,800 m² or ground-mount |
| Converter arrangement | Single unit | Single unit or two parallel | Multiple units, engineered arrangement |
| Storage pairing | Sized per project; reference on request | 215 kWh reference configuration | Sized per project — PV/generator or PV/grid hybrid design |
| Design effort | Light | Moderate | A design project of its own |
How to read this table: the roof-area row is a sanity check, not a starting point. Sites first disqualify themselves on the converter row — a 250 kW peak cannot be carried by a 100 kW converter regardless of battery size, and the site will trip to bypass. Area, orientation and roof load limit then set the PV ceiling, as described in the sizing method.
How this is calculated, and what we assume
The peak-demand bands above are design rules of thumb, not product limits. The rigorous sequence is:
Converter ≥ peak demand + starting margin, then battery = critical load × backup duration ÷ (efficiency × usable window). Two independent checks, and both must pass.
| Input | Where it comes from | What it decides |
|---|---|---|
| Highest 15/30-min average demand | Interval meter data, or a week of logged readings | Converter rating and the size class |
| Largest motor starting current | Motor list with start methods | Converter overload requirement, or soft starters |
| Critical load × backup duration | Critical circuit list and your outage policy | Battery capacity, within the class |
| Usable roof/land area | Site survey or drawings | PV ceiling — often the binding constraint before demand is |
A caution that recurs in tender documents: sizing from monthly kWh. A site consuming 600 kWh/day is not automatically a "100 kW site" — the split between day and night, and the peak within the day, decide it. Two sites with identical monthly consumption can need different size classes.
Project evidence
Anonymised references at each scale — region, configuration, load profile and status — are listed on the configuration page. Where the customer has approved disclosure, the reference also carries the site and the result.
When this comparison is not the right tool
- Your demand data is interval-based and shows peaks that swing between classes month to month: size the converter on the sustained upper band and treat the comparison as a starting sketch.
- Your driver is outage protection rather than bill reduction: the topology decision (hybrid vs off-grid) comes first, because it changes the battery budget far more than the size class does.
- Your roof cannot carry even the smallest class: ground-mount or a storage-only design changes the whole comparison.
Next step
Send one week of interval data (or twelve monthly bills if that is what exists) and the critical load list. We will tell you which class you are actually in — and whether you are in one at all.